100 years ago, titans suddenly appeared on Earth. Soon, human civilization veered on collapse due to the titans. Humans then built a giant wall to defend themselves. Within the giant walls, humans lived in peace, but, 100 years later, the giant wall is broken.

Humanity is under attack by human-mimicking flesh-eating alien parasites. One parasite bonds with his young high school student host, and he convinces the parasite to help him stop the others.

It is only at their sister's and mother's funeral when a woman meets her niece after many years. The niece is now a grown girl. The sister takes on the task of informing the deceased's friends of the death while the daughter cannot bring herself to symbolically accept the demise of her mother. In the midst of all this an old flame messages the sister to say he is still in love with her, but is he messaging the living sister or the dead one?